a) Field of the Invention
The present invention relates to a measuring endoscope, which may be inserted in narrow spaces such as interiors of organs of human bodies and interiors of industrial appliances for measuring concavities and convexities on the surfaces thereof.
b) Description of the Art
There is conventionally known a measuring endoscope which allows measurements of concavities and convexities on surfaces of organs of human bodies and so on by utilizing linear diffraction patterns of laser light formed with a diffraction grating. These diffraction patterns are projected onto a surface of an object to be observed by a projector lens for forming an image of the object. When this image is observed with parallax on an imaging device such as a solid-state image pickup device, the original linear diffraction patterns are deformed on the image of the object depending on shapes of the concavities and convexities on the surface. Accordingly, the measuring endoscope permits measuring the shapes of the concavities and convexities on the surface of the observed object by calculating, on the basis of video signals provided from the imaging device, displacement of lightness on each portion of the diffraction patterns on the surface of the object from lightness on a standard point.
Further, there is available the fringe scanning method as a method for measuring surfacial shapes of objects. This measuring method features high measuring accuracy, allows measurement independent of nonuniformities in contrast and permits automatic discrimination between concavities and convexities. Though the fringe scanning method is adopted for inspecting shapes of optical elements such as lenses, it is considered adequate to apply the projection type fringe scanning method to the measuring endoscope since this application makes it possible to obtain information on concavities and convexities which are not influenced by discoloration on diseased locations.
However, the measuring endoscope of this type poses a problem that it does not permit accurate measurement of surfacial shapes when the linear diffraction patterns are non-uniform in contrast due to colors, depths of concavities and convexities, etc. on the surfaces of objects to be measured. Further, there have been no conventional examples to apply the projection type fringe scanning method to measurements of shapes of objects within narrow spaces or to compact optical systems having small diameters such as endoscopes.